Expanding on 'dawg, it's generally only profitable to rent if you're a company devoted only to renting, and the regulatory regime punishes the landlord with only a few units. This is because rents are not market-based, but instead are based on "use value" (bruksvärde). A 19th C apartment in the middle of the city can theoretically be worth "less" from a rental perspective than a newly built apartment in the suburbs.
Any annual rent increases are set via a form of collective bargaining, and if a landlord charges more, the renter is entitled to their money back.
The upshot of this is that it's much more profitable to buy a rental building and flip it to the renters via a bostadsrättsförening (a bit like a condo) or to only build to sell.
No, the landlords in these cases own the whole building, not just a few flats. If you own the whole building then you can of course rent out the flats in that building. But if you just own a couple of flats in the building, then you generally cannot easily rent them out.
